.TH std::make_from_tuple 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::make_from_tuple \- std::make_from_tuple

.SH Synopsis
   Defined in header <tuple>
   template< class T, class Tuple >           \fI(since C++17)\fP
   constexpr T make_from_tuple( Tuple&& t );  (until C++23)
   template< class T, tuple-like Tuple >      (since C++23)
   constexpr T make_from_tuple( Tuple&& t );

   Construct an object of type T, using the elements of the tuple t as the arguments to
   the constructor.

   Given the exposition-only function /*make-from-tuple-impl*/ defined as follows:
   template<class T, tuple-like Tuple, std::size_t... I> // no constraint on Tuple
   before C++23
   constexpr T /*make-from-tuple-impl*/(Tuple&& t, std::index_sequence<I...>)
   {
       return T(std::get<I>(std::forward<Tuple>(t))...);
   }

   The effect is equivalent to:
   return /*make-from-tuple-impl*/<T>(
       std::forward<Tuple>(t),
       std::make_index_sequence<std::tuple_size_v<std::remove_reference_t<Tuple>>>{}
   );.

   If

     * std::tuple_size_v<std::remove_reference_t<Tuple>> is 1 and                (since
       std::reference_constructs_from_temporary_v<                               C++23)
           T, decltype(std::get<0>(std::declval<Tuple>()))> is true, or

     * std::is_constructible_v<T, decltype(std::get<I>(std::declval<Tuple>()))...> is
       false,

   the program is ill-formed.

.SH Parameters

   t - tuple whose elements to be used as arguments to the constructor of T

.SH Return value

   The constructed T object or reference.

.SH Notes

   Tuple need not be std::tuple, and instead may be anything that
   supports std::get and std::tuple_size; in particular, std::array and   (until C++23)
   std::pair may be used.
   Tuple is constrained to be tuple-like, i.e. each type therein is
   required to be a specialization of std::tuple or another type (such as (since C++23)
   std::array and std::pair) that models tuple-like.

   Due to guaranteed copy elision, T need not be movable.

      Feature-test macro      Value    Std         Feature
   __cpp_lib_make_from_tuple 201606L \fI(C++17)\fP std::make_from_tuple

.SH Example


// Run this code

 #include <iostream>
 #include <tuple>

 struct Foo
 {
     Foo(int first, float second, int third)
     {
         std::cout << first << ", " << second << ", " << third << '\\n';
     }
 };

 int main()
 {
     auto tuple = std::make_tuple(42, 3.14f, 0);
     std::make_from_tuple<Foo>(std::move(tuple));
 }

.SH Output:

 42, 3.14, 0

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

      DR    Applied to              Behavior as published              Correct behavior
   LWG 3528 C++17      cast containing reinterpret_cast etc. was       prohibited
                       allowed in the case of 1-tuple

.SH See also

   make_tuple       creates a tuple object of the type defined by the argument types
   \fI(C++11)\fP          \fI(function template)\fP
   forward_as_tuple creates a tuple of forwarding references
   \fI(C++11)\fP          \fI(function template)\fP
   apply            calls a function with a tuple of arguments
   \fI(C++17)\fP          \fI(function template)\fP
